This invention relates to improved benzoxazinone UV absorbers. More specifically, this invention relates to low color, low sodium benzoxazinone UV absorbers especially suitable for high transparency applications, and the process for making such absorbers.
Exposure to sunlight and other sources of ultraviolet (UV) radiation is known to cause degradation of a wide variety of materials, especially polymeric materials. For example, polymeric materials such as plastics often discolor and/or become brittle as a result of prolonged exposure to UV light due primarily to a reduction in the molecular weight of the polymer. Accordingly, a large body of art has been developed directed towards materials such as UV light absorbers and stabilizers, which are capable of inhibiting such degradation.
One important application that uses UV absorbers is optical quality lenses, such as prescription eyewear. Preferably, polycarbonates are used in lenses due to their toughness and transparency over acrylics and other amorphous polymers. Clarity and color are important parameters in this application and absorbers are needed to screen UV light up to the 380 nm region without affecting the visible region over 400 nm. Some benzoxazinone UV absorbers, such as 2,2,-p-phenylenebis(3,1-benzoxazine-4-one), are preferred in this application because they meet these UV requirements.
However, commercial benzoxazinone compounds like 2,2xe2x80x2-p-phenylenebis(3,1-benzoxazine-4-one) have problems due to their method of manufacturing. These methods are disclosed in U.S. Pat. Nos. 3,989,698 and 4,446,262.
One method of producing 2,2xe2x80x2-p-phenylenebis(3,1-benzoxazine-4-one) is by reacting anthranilic acid, sodium carbonate, terephthaloyl dichloride and acetic anhydride (example 19 in U.S. Pat. No. 4,446,262). However, this method results in a high concentration of sodium ion (Na+) impurities in the benzoxazinone product, which severely degrades polycarbonates.
Another method to produce 2,2xe2x80x2-p-phenylenebis(3,1-benzoxazine-4-one) is by reacting isatoic anhydride with terephthaloyl dichloride (Example 24 in U.S. Pat. No. 3,989,698). However, a problem with prior art commercial products using this method is that they have a high degree of color that limits their desirability to be used in optical lens and other high transparency applications.
Therefore, there is a need to produce a low color, low sodium benzoxazinone compound, which is suitable for use in high transparency and other polymeric applications.
The present invention relates to a compound of Formula I: 
where n is 1 to 3, R1 is a direct bond or a hydrocarbon residue having a valence of n which may further contain a heteroatom, and R2 is hydrogen, halo, nitro, C1 to C8 alkyl, C1 to C8 alkoxy, or C1 to C8 alkenyloxy. These compounds have a yellow index less than about 0 and a sodium concentration less than about 50 ppm.
This invention also relates to a process for preparing the compound of Formula I comprising the step of reacting an isatoic anhydride with approximately stoichiometric amounts of an acylating compound, where the isatoic anhydride is purified by re-crystallization or other purification methods.